ASTRONOMISCHE NACHRICHTEN. IT 3771. Band 158. 3- The Nebula about Nova Persei 1901 9. By 1;: W. Very. In a letter to the Editor of the Astr. Nachr. No. 3736 *esemble those of a series of explosions produced by a dated Aug. 23, 1901, MM. Flammarion and Antoniadi an- brce of gradually waning energy. nounced the discovery of a nebulous aureole, 6' in diameter, The following considerations prove, however, that the around Nova Persei 1901. Dr. Max Wolf immediately con- nebulous streaks are not portions of spiral streams emanating firmed this observation, and, in addition, recorded a further from the star under the action of any ordinary hydrodynamic extension to a distance of 5' from the nova, at least on pressures. Great mass would be needed in this case to the south side and somewhat to the east, the nebuloiis prevent the dissipation of the star simply by the centrifugal material being excessively faint, and yet rich in structure. force of rotation. A body having a mass 1500 times as Although these early observations have been questioned on great as our sun's and a diameter of IOOOOOOO miles could the ground that the aureole may have been only an instru- rotate once in 2 hours without generating an equatorial mental effect, due to the preponderance of ultraviolet light surface -motion greater than the parabolic velocity, but some in the rays from this star, and to the use of an imperfectly such speed of rotation would be needed to produce spiral corrected telescope, the reality of the more extensive streamers by combination with the radial velocities spectro- appendage and its nebulous character have now been com- scppically observed ; for the spectrum of Nova Persei I 90 I pletely confirmed from photographs with powerful reflecting exhibited at the violet hydrogen line (HI, displacements telescopes at the Yerkes and the Lick Observatories. of 30 tenth-meters, which, if due to motion in the line of The nebula photographed by Mr. Ritchey 2) has every sight, correspond to a mean velocity of 2193 km, or 1363 appearance of being concentric with the star and an ap- miles per second. A radial movement of this amount, en- purtenance of that body. It also has a structure which is during unchanged for 210 days, from the appearance of either spiral, or composed of several annuli, or fragments the star, February 22, to the date of Ritchey's first photo- of annuli, probably lying in different planes and thus seeming graph, September 20, 1901,should carry the erupted gases to intersect. The outer parts of the nebula are strongest to an extreme distance from the star of 3.98 x (10)10 km. on the southern side where they consist of parallel or con- The radius of the nebula, as photographed by Ritchey, is centric segments about apart. On the following side, about 480", whence I" = 82900000 kilometers, and the in the September photograph, there are four concentric parallax (on these assumptions) would be 1180. Dr. Cour- segments of annulli, or perhaps of spherical shells, about voisier of Heidelberg has published meridian-circle observations xlf2' apart. (A. N. 3753) which prove that the parallax of the nova is To see if it would be possible to account for these certainly less than of a second of arc, and in the United features on the supposition that they are remnants of stellar States, Messrs. R. H. Tucker and R. G. Aitken of the Lick envelopes thrown off by periodical hydrogen eruptions, I made Observatory, and Chase of New Haven have each arrived some preliminary computations with various assumptions. at the same conclusion independently. Consequently the Father Hagen 3) has given a light-curve of the nova nebulous streamers cannot have been produced directly by from a compilation of the results of many observers, which explosive outbursts of hydrogen. To form the outer annulus indicates that at the beginning the period of luminous variation shown in Mr. Ritchey's photograph of September 20 at a may have been as short as I day, and that it afterwards distance of 7 to 8 minutes of arc, a mean radial movement increased rapidly to a mean period of about 3 days, which of I' in 4 weeks would be required. Comparison with Dr. has now further lengthened to 41l2 or 5 days. Wolf's observation indicates an outward or expansive motion The concentric structure on the outskirts of the nebula also of I' in the same time on the south side, if we assume on the southern side, which by supposition has been first that both measurements relate to the same nebulous detail. produced, is much finer, that is to say, the streaks are closer Perrine's observation of a motion at four different points together than those nearer the center, and as if pertaining in the nebula, which he has been able to identify with to operations in a more rapid sequence. The phenomena structures shown in Ritchey's first photograph, through one l) Read at the fourth annual meeting of the Astronomical and Astrophysical Society of America. Dec. 31, 1901. z, 'Astrophysical Journal, vol. 14, plates XVIn and XIX, November, 1901. s, Rev. J. G. Hagen, S. J. .Preliminary Light Curve of Nova Persei 1901. From February 22 to May 1.a Georgetown College Observatory Circular. 3 35 37 I 36 and one half minutes of arc in fortyeight days, demonstrates lot less than of a second of arc, and its maximum a velocity of the same order, which is further confirmed by %stance not over 124 light-years. Its parallax ought, there- Ritchey's photograph of November I 3. bre, to be within the range of possible careful measurement. Mr. Ritchey finds that the entire southern half of the All novae that have appeared up to the present time nebula has been expanding rapidly and nearly radially. lave been associated with the Milky Way. If it be admitted Perrine's observations differ slightly. >The displacementsc ihat Nova Persei is a constituent member of the galactic he says ,agree well.. .The directions are not so consistent, jtream, we have now, and for the first time, an approximate and could perhaps be explained by irregular niotions in the dea of the distance to the Milky Way which, in the con- nebulous mass. c Mr. Ritchey's later photograph shows that stellation Perseus, cannot be more than about IZOO million careful discrimination will be needed to distinguish changes million kilometers away. of shape in minor details from general movements. It appears probable that like the tails of comets, the The fact of motion in nebulous matter is thus abund- ,urninous bodies of the gaseous nebulae require only a small antly demonstrated, but it is equally certain that this motion miass of excessively diluted material to produce their shining. is not that which we have been seeking, and due to explosive eruption of gases in large masses. It is rather to an electric repulsion of individual atoms or corpuscles, similar to that Let us now examine the evidence to be deduced from which gives the cathode rays in a Geissler's tube, or perhaps :he spectroscopic measurements. The structure of the hy- to motions initiated by that pressure of light which has now drogen bands in the spectrum of the nova has exhibited been demonstrated by the experiments of Nichols and Hull, great complexity and variability. In general, each band has that we must look for an explanation of the rapidly growing been found to consist of a broad region of absorption on and fast fading nebula. The annuli may be gigantic striae the violet side, with local intensificatibns of absorption, or similar to those seen in electrified tubes containing rarefied dark lines, which are repeated in the same order of position gases, and may be produced by chemical combination of or intensity in nearly all of the bands. The half towards different sets of atoms or corpuscles, thrown off during the red end of the spectrum is always bright, and has been alternating phases of the eruption, and electrically or lumin- commonly subdivided into from two to four or more minor ously repelled at different speeds depending on the nature bands, separated by absorption lines in the same relative of the particles; or if spiral motion should be certaidy positions in every one of the hydrogen bands, with trifling indicated, we may surmise that there has been some sort exceptions which may be explained by the superposition of of cathode discharge along, or (more accurately) around spectral lines of other substances. The displacements of magnetic lines of force. similar subdivisions, according to the measures of Campbell Professor J. J. Thomson 1) has found that the speed and Wright, are proportional to the wave-length, and are of the electric discharge, when striae are produced, approaches consequently due to motion in the line of sight; and each that of light. Although no such velocity is implied for the subdivision of a band must be attributed to light emanating atoms in vacuum tubes, it is possible that, in free space, from, or absorbed by the atoms of an individual gaseous electrified particles of less than atomic dimensions, namely, mass or stream having a particular velocity in the line of sight. those Thomsonian corpuscles which appear to constitute The gathering of the principal dark subdivisions on the very substance of static electricity, may exhibit velocities the violet side, and of the bright components on the red of this order. Assuming the velocity of light as an outside side of each band, without any exception, may all be ex- limit for the speed of particles thrown off from the nova plained as due to the presentation of successive shells of by electric repulsion, it follows that the parallax of Nova hot gas, periodically expelled from the star, and arranged Persei I 90 I , corresponding to the dimensions of the bound- concentrically around it.